Operation, High Limit Controller | Honeywell L7248A,C,L, L7224A,C

L7224A,C; L7248A,C,L OIL ELECTRONIC AQUASTAT® CONTROLLERS

Table 4. Display readout definitions.

Text	Description	Display
Err	Error Code (if one is present)	

bT	Boiler Temperature	

HL	High Limit 1	
HdF	High Limit Differential	

LL	Low Limit (L7224 only)	

Ldf	Low Limit Differential (L7224 only)	

tt	Local Thermostat Status	

ttE	EnviraCOM Thermostat Status	

brn	B1 (Burner) output (ON or OFF)	

Cir	C1 (Circulator) output (ON or OFF)	

ZC	ZC (Zone Control) output (ON or OFF)	

Zr	ZR (Zone Request) Call for HEAT (ON or OFF)	

ELL	External Low Limit Enabled (L7248L only)	

duu	ZR Configured as Domestic Hot Water	
	Request (L7224, L7248L only)
ASC	Anti Short-Cycle Timeout	

bSP	Boiler Set-Point 2	
dhc	DHW Module Connected 3 (YES or NO)	
ot	Outdoor Temperature 2	
otL	Outdoor Temperature Low 2	
otH	Outdoor Temperature High 2	
btL	Boiler Temperature Low 2	
bP	Boost Period 2	
bS	Boost Step 2	
UUS	Warm Weather Shutdown Temperature 2	

1Display shows local setting; not the setting as modified by an external enviracom control.

2Settings are viewable only if the outdoor reset module and out- door temperature sensor are installed and functioning properly.

3Settings are viewable only if the domestic hot water module and sensor are installed and functioning properly.

Operation

The L7224 and L7248 models can be in any of four operational states: Normal, High Limit, Low Limit and Error. The controller moves back and forth from

High Limit to Normal to Low Limit state as part of normal operation. Only devices having High Limit settings are restricted to the High Limit and Normal states. However, the controller will enter the Error state when there is an abnormal condition. The operating states are:

1.Normal: Boiler temperature went below the High Limit setting (minus the Differential) and has not exceeded the High Limit setting; or, the boiler temperature went above the Low Limit setting and

has not gone below the Low Limit setting (minus the Differential); or, ZR input is not powered with 120 Vac (only L7248L with ELL set On).

2.High Limit: Boiler temperature went above the High Limit setting and has not dropped below the High Limit setting (minus the Differential).

3.Low Limit: Boiler temperature went below the Low Limit setting (minus the Low Limit Differential) and has not gone above the Low Limit setting; or, ZR input is powered with 120 Vac (only L7248L with ELL set On).

4.Error: The controller has detected an error condition (e.g., open sensor) and has shut down the burner output. The ZC output is energized. The controller continues to monitor the system and automatically restarts if the error condition clears. Refer toTable 4.

The operating sequence for the L7224/L7248 is shown in Table 6–9.

High Limit Controller

The High Limit opens and turns off the burner when the water temperature reaches the setpoint. The High Limit automatically resets after the water temperature drops past the setpoint and through the Differential. The L7248 models have High Limit Differential presets of 15 °F

(8 °C). The L7224 models have High Limit Differential presets of 10 °F (6 °C).

Low Limit and Circulator

Controller

On a temperature rise, with the adjustable Differential at the default setting of 10 °F (6 °C), the burner circuit breaks and the circulator circuit makes (assuming no call for heat is present) at the Low Limit setpoint. On a temperature drop of 10 °F (6 °C) below the Low Limit setpoint, the burner circuit makes and the circulator circuit breaks. See Fig. 7.

SWITCH BREAKS ON

TEMPERATURE RISE.

BURNER TURNS OFF.

HIGH LIMITCIRCULATOR OPERATES

SETTING ON A CALL FOR HEAT.

	L7224: 10°F (6°C)
	DIFFERENCE	SWITCH MAKES ON
	L7248: 15°F (8°C)	SWITCH MAKES ON
	DIFFERENCE	TEMPERATURE FALL.
		BURNER OPERATES ON A
		CALL FOR HEAT.
	LOW LIMIT	WITH NO HEATING
	SETTING	WITH NO HEATING
	10ºF (6ºC)	DEMAND, SWITCH BREAKS
	10ºF (6ºC)	ON TEMPERATURE RISE. 1
	DIFFERENCE	ON TEMPERATURE RISE. 1
		SWITCH MAKES ON
		TEMPERATURE FALL,
		BURNER IS ON TO
		MAINTAIN MINIMUM
		WATER TEMPERATURE.
		CIRCULATOR IS OFF.

1WHEN WATER REACHES LOW LIMIT SETTING, THE BURNER SHUTS OFF OR THE CIRCULATOR PUMP STARTS (WHEN CALLING FOR HEAT).

M23364

Fig. 7. Setpoints and differentials.

Anti Short-Cycle Feature

The Anti Short-Cycle feature allows for field selection of a delay time between burner cycles. Should a call for heat occur following the end of the previous heat cycle and before the Anti Short-Cycle delay time is expired, the circulator will be allowed to run, but the burner will be held off until the time has elapsed. The range of the Anti Short- Cycle time is from OFF to five minutes.

68-0281EFS—05